An organic EL device is a spontaneous light emitting device which utilizes the principle that holes injected from an anode and electrons injected from a cathode are recombined in response to the applied electric field and the recombination energy causes the light emission from a fluorescent substance. Therefore, it is important for increasing the efficiency of an organic EL device to develop a compound which transports electrons or holes into a light emitting zone efficiently and facilitates the recombination of electrons and holes.
The device performance of organic EL devices has been improved by making a hole transporting layer into two-layered structure which includes a first hole transporting layer and a second hole transporting layer from the anode side. The first hole transporting layer is generally required to be excellent in the hole injection ability into the second hole transporting layer.
For example, Patent Literature 1 discloses an organic EL device wherein a monoamine compound having an ortho-substituted phenyl group is used as the material for the layer adjacent to the light emitting layer.
Patent Literature 2 discloses an organic EL device wherein a monoamine having a fluorene group is used as the material for the first hole transporting layer.